Stabilization of chlorinated solbents



United States ?atent 2,944,083 STABILIZATION F CHLORINATED SOLVENTS Otto S. Kauder, Jamaica, N.Y., assignor to Argus Chemical Corporation, a corporation of New York No Drawing. Filed Oct. 31, 1958, Ser. No. 770,942 8 Claims. (Cl. 2'60652.5)

- This type of decomposition, conveniently referred to as 'condensanon-decomposition, is even more severe with methyl chloroform than with trichloroand perchloroethylene.

The second type decomposition is observed when the solvent is exposed to strong light in the presence of air, and much more severely when the solvent or its vapor comes in contact With metals at elevated temperatures, such as in a vapor-degreasing operation. Among the metals most active in promoting this oxidation-decomposition are iron, copper, and alloys of these metals. This decomposition leads to formation of HCl and acid chlorides and is less severe with methylchloroform than with triand perchloroethylene.

The prior art has found certain ways of dealing with both types of decomposition to a certain extent. Condensation-decomposition is substantially reduced by the use of various organic oxygen compounds, e.g. organic epoxides of suitable boiling point, such as butylene oxide and epichlorohydrin.

A large variety of organic compounds has been recommended for stabilizing degreasing solvents against oxidation-decomposition. I mention aliphatic and aromatic amines, nitriles, pyridine and its homologues, hexamethylene tetramine, phenol and derivatives thereof, pyrroles and other heterocyclic compounds.

While some of these compounds are truly efiective in preventing the formation of acidic degradation products, most of them do not meet all the requirements for a satisfactory stabilizer for degreasing solvents.

An acceptable stabilizer should-in addition to providing the necessary degree of stabilization-have about the same volatility as the solvent to be stabilized. It should not be so strongly alkaline that its volatility is appreciably reduced in the presence of acidic materials. It should not be removed from the solvent by water extraction. It should not promote the formation of corrosion products or insoluble sludges. It should also afford the possibility to the user to ascertain the concentration of available stabilizer during use.

All the hitherto available stabilizers are deficient in one or more of the above-mentioned requirements.

Even the pyrroles, which may be considered the best stabilizers available at present for protecting degreasing solvents against oxidation-decomposition, have a tendency to form a dark purple sludge, the presence of which may be detrimental to prolonged use of the solvent.

It is an object of this invention to stabilize degreasing solvents against both types of decomposition. It is a further object to provide such degreasing solvents containing a stabilizer Volatile with the solvent even in the presence of oils, greases, and fatty acids.

It is another object to provide a stabilized degreasing ice solvent of low alkalinity, whose degree of stability can be gauged during use by simple titration.

Still another object of the invention is a method of preparing in situ a concentrate of the stabilizer in the solvent suitable for. dilution with unstabilized solvent for the final use.

Other objects and advantages will become apparent from the following detailed description.

These objects are accomplished by using as stabilizer a condensation product obtained by reaction of formaldehyde or acetaldehyde with a primary amine having not more than three carbon atoms. The amount of the stabilizer to be used is from 0.01 to 2% by weight of the solvent.

The condensation products to be used. as stabilizers according to the invention are known per se. The originally formed Schiifs bases trimerize spontaneously to cyclic compounds. For the product formed from formaldehyde and methyl amine, the formula. of the cyclic compound is the following:

Ht-JCN NCHz H3O Hz NCH:

Trimethyl-1,3,5-hexahydrotriazine These cyclic trimers are generally considered to be stable compounds. The above-mentioned compound, for instance, is described as a liquid boiling at 166 C. at normal pressure, the ethyl homologue boiling at 250 C. Until recently, all efforts to prepare the monomeric Schifis bases from an aldehyde with one to two carbon atoms and an amine of not more than three: carbon atoms have furnished only the cyclic trimers. 'Lately, the prep aration of monomeric N-methylmethylene imine by pyrolysis of the trimer under special rather severe temperature conditions has been disclosed in US. Patents 2,729,- 679 and 2,729,680.

It is therefore a surprising discovery that the condensation products made from formaldehyde and acetaldehyde with primary amines having up to three carbon atoms have suflicient volatility to make them suitable stabilizers for chlorinated degreasing solvents. Thus in a preparation of 1,3,5-triisopropylhexahydrotriazine from formaldehyde and isopropyl amine, about half the material was distilled at 80 C. and 15 mm. pressure. Both the distillate. and the residue were active stabilizers for trichloroethylene, and passed into the distillate when samples of the stabilized trichloroethylene were mixed with one-tenth volume of oleic acid and distilled. until of the solvent had come over.

It should be particularly emphasized that while simple amines are ineifective as stabilizers in the condensationdecomposition, which is particularly important in the case of methylchloroform, the amine-aldehyde condensation products have a satisfactory stabilizing effect.

The amine-aldehyde condensation products prepared by conventional methods are fully satisfactory as stabilizers for the purposes of this invention. However, it is especially advantageous to prepare these compounds in situ illustration and not of limitation and that many changes in the details can be made without departing from the spirit of the invention.

. Before entering into the description of the examples, a method will be described, by which I removed from commercial degreasing solvents the stabilizers contained therein, since unstabilized solvents are not available.

One liter of trichloroethylene was Washed in succes-. sion, once with 130 ml. of 40% aqueous sulfuric acid, then twice with 130 ml. of concentrated sulfuric acid, then twice with 130 ml. water, then once with 130 ml. of a 1:1 dilution of concentrated aqueous ammonia, and twice more with 130 ml. of water. The solvent layer was drawnoft and distilled from a still containing about 10 g. or" potassium carbonate to prevent decomposition of the solvent during distillation. The first runnings of distillate contained some water, and were discarded. About 800 ml. of dry trichloroethylene, B.P. 86.588 C. were obtained and used for stability tests as described below.

Commercial perchloroethylene and methylchloroform were treated in the same way to eliminate the stabilizer contained in the products of the market.

EXAMPLE 1 Preparation of a condensation product 150 ml. 40% formaldehyde solution (2 mol) were stirred and cooled in an ice bath while an equimolecular quantity of isopropyl amine (118 g.) was added slowly. Stirring was continued one hour after the end of addition of the amine, and the layers were then separated. The upper layer containing the condensation product was dried over potassium carbonate and stripped under 15 mm.

pressure to a pot temperature of 110 C. The residue Preparation a stabilizer concentrate (a) To a stirred mixture of 50 ml. trichloroethylene and 75 ml. (1 mol) 40% formaldehyde solution, 63.4 g. of a 71.7% aqueous ethylamine solution (1 mol) were addedslowly with cooling in a pan of water to keep the temperature from rising above 45 C. One hour after the end of the addition, the layers were separated, and the aqueous layer was extracted with two 50 ml. portions of trichloroethylene, combining the extracts with the first solvent layer. Titration showed a 91% yield of the condensation product in the trichloroethylene solution. The final product contains about 34 g. condensation product in 100 ml. solvent.

(b) The procedure (a) was repeated, but the ethylamine was replaced by 77 ml. of a 40% methylamine solution. The yield of condensation product in the trichloroethylene solution was 34%. The final product contains about 10 g. condensation product in 100 ml. solvent.

(0) The procedure (a) was repeated using 59 g. an- I EXAMPLE 3 Comparative tests for stabilization against.

oxidation-decomposition A test to measure the extent to which trichloroethylene will undergo metal-catalyzed oxidation-decomposition under conditions simulating conditions of use in degreasing is described in Federal Specification OT-634A, titled 'Irichloroethylene, technical, dated April 17, 1956. In this test, a 200 ml. sample of the solvent is illuminated and heated under reflux by means of a 150 watt electric light bulb while a stream of oxygen, which has previously passed through a bubble counter filled with water, is passed into the boiling solvent. A strip of steel, 2 x /2 x inches, is suspended in the vapor and another strip, 4 x A x inches, is placed in the boiling liquid. The metal-catalyzed oxidation is allowed to proceed for 48 hours; at the end of this time the solvent is cooled to room temperature and a sample titrated with 0.01 11 NaOH solution in order to determine the amount of acid formed in the oxidation. Federal Specification requires a maximum of 0.02% hydrochloric acid after the stability test.

The following Table No. 1 illustrates the stability of trichloroethylene stabilized with various stabilizers. In test I, the solvent samples were immediately submitted to the test as described above. In test II, the solvent samples were distilled and a center cut submitted to the test. In test III, 300 ml. portions of solvent were mixed with 30 ml. oleic acid and distilled until 240 ml. had been collected. These distillates were then submitted to the test.

The quantity of the various stabilizers is expressed in weight percent for g. solvent. The stabilizers according to the invention are being used in a quantity of 0.001 mol per 100 g. solvent, so that their alkalinity is equivalent to 0.04 g. NaOI-I. Thus, the product of Example 1 was applied in a concentration of 0.071 g. in 100 g. solvent and the products of Example 2 (a), (b), c), and (d) in the concentration determined by titration to beequivalent.

TABLE 1 Test I Test II Test, I II Stabilizer Percent; Appearance Percent Appearance Percent Appearance H01 H01 7 H01 None 0.2 light: yellow clean"- I Diisopropylamine, 0.025+Bunone do none light yellow clean... 0.1 light yellow clear.

tylene oxide, 0.05. Pyridine, 0.1 0. 025 dark red sludge. O. 04 dark red sludge. 0. 04 dark red sludge. Aniline, 0.05-l-Epichl0r0hy- 0.003 deep yellow, some 0.1 yellow 0. 1 yellow.

drin, 0.25. rust. I

0. 006 light yellow elear.. 0.1 light yellow 0. 1 light yellow. 0.001 purple dark speoks 0. 004 purple dark specks 0. 004 purple dark specks. 0.001 deep red flufiy pre- 0.001 deep red flufiy pre- 0.001 deep red flufly precipitate. pit e. cip ate. Product of Example 1 0 slightly cloudy 0 slightly cloudy. Product of Example 211 0 do 0 D0. Product of Example 211 0 0 Do. Product of Example 20 0 0 Do. Product of Example 2d Q 0 Do.

l t h These results show the superior performance of the stabilizers according to the invention.

EXAMPLE 4 The tests described in Example 3 were repeated with perchloroethylene instead of tn'chloroethylene. The results were practically identical.

EXAMPLE 5 It has also been found that it is possible to obtain very good stabilizing effects, when, instead of a single aldehyde-condensation product, as described, mixtures of two or more such condensation products were used as stabilizers in equal total amount.

EXAMPLE 6 Comparative tests for stabilization against condensationdecomposition 250 ml. samples of trichloroethylene containing 0.25 g. butylene oxide per 100 g. solvent plus various stabilizers specified below along with 0.5 g. anhydrous aluminum chloride were refluxed 10 minutes, cooled, and filtered. Additional samples were subjected to the distillation procedures of test II and test III described above, before being refluxed with aluminum chloride. The epoxide remaining in the filtrate was determined by allowing the epoxide to react with excess hydrogen chloride in methanol and back-titrating the unreacted acid. The following Table II shows the remaining epoxide as a percentage of the original epoxide concentration.

The products of Examples 1, 2a and 2b were used in the same amounts as given in Example 3.

TABLE II Stabilizer Test I Test; II Test; III

None 12 15 19 Diisopropylamine, 0.025 18 18 18 Pyridine, 0.1 12 14 19 N-Methylpynole, 0.1 27 29 30 Product of Example 1. 45 49 38 Product of Example 2a- 43 44 36 Product of Example 21: 40 38 88 These results show superior performance by the products according to the invention in stabilization against condensation-decomposition.

EXAMPLE 7 Stabilization against condensation-decomposition of methylchlaroform kept in contact with aluminum for 10 days without evidence of decomposition.

What I claim is:

1. A stabilized chlorinated aliphatic solvent having a boiling point below 130 C. containing per g. solvent 0.01 to 2 g. of a condensation product of an aidehyde of the group consisting of formaldehyde and acetaldehyde with a primary amine containing 1-3 carbon atoms.

2. Stabilized trichloroethylene containing per 100 g. thereof 0.01-2 g. of a stabilizer consisting of a condensation product of an aldehyde of the group consisting of formaldehyde and acetaldehyde with a primary amine containing 1-3 carbon atoms.

3. Stabilized perchloroethylene containing per 100 g. thereof 0.01-2 g. of a stabilizer consisting of a condensation product of an aldehyde of the group consisting of formaldehyde and acetaldehyde with a primary amine containing 1-3 carbon atoms.

4. Stabilized methylchloroform containing per 100 g. thereof 0.01-2 g. of a stabilizer consisting of a condensation product of an aldehyde of the group consisting of formaldehyde and acetaldehyde with a primary amine containing 1-3 carbon atoms.

5. Stabilized chlorinated aliphatic solvent having a boiling point below C. containing per 100 g. solvent 0.01 to 2 g. of a condensation product of ethylamine and formaldehyde.

6. Stabilized chlorinated aliphatic solvent having a boiling point below 130 C. containing per 100 g. solvent 0.01 to 2 g. of a condensation product of methyl amine and acetaldehyde.

7. Stabilized chlorinated aliphatic solvent having a boiling point below 130 C. containing per 100 g. solvent 0.01-2 g. of a mixture of condensation products of an aldehyde selected from the group consisting of formaldehyde and acetaldehy'de with a primary amine containing 1-3 carbon atoms.

8. A method for making a stabilized chlorinated aliphatic solvent having a boiling point below 130 C. which comprises preparing a stabilizer concentrate by condensing in said solvent an aldehyde of the group consisting of formaldehyde and acetaldehyde and a primary amine containing 1-3 carbon atoms, allowing the mixture to react at temperatures below 450 C. until the condensation is completed, using the aldehyde and the amine in equimolecular proportions and such quantities that the final product contains from 10-50 g. per 100 ml. solvent, and subsequently diluting it to the concentration desired for use with unstabilized solvent.

References Cited in the file of this patent UNITED STATES PATENTS Great Britain Feb. 8, 1949 

1. A STABILIZED CHLORINATED ALIPHATIC SOLVENT HAVING A BOILING POINT BELOW 130*C. CONTAINING PRODUCT OF AN ALDEVENT 0.01 TO 2 G. OF A CONDENSATION PRODUCT OF AN ALDEHYDE OF THE GROUP CONSISTING OF FORMALDEHYDE AND ACETALDEHYDE WITH A PRIMARY AMINE CONTAINING 1-3 CARBON ATOMS. 